The best known methods for bitumen separation from oil sands are the hot water or Clark process and the cold or diluent water processes.
In the hot water process, tar sand, steam and caustic soda are fed into a rotating tumbler or drum to form a slurry at about 80.degree.-85.degree. C., with 20-25% wt. water. In the tumbler the bitumen is released from the sand particles. After screening, to eliminate oversized clay lumps and rock fragments, the slurry is water-flooded and then continuously pumped into a primary separation vessel, where most of the sand particles settle, oil rises to the top and an aqueous middling stream, with fine silt and clay, is withdrawn and secondarily processed to recover entrained oil. Cold water processes include mixing and slurrying oil sands with a hydrocarbon diluent and (or without) process control additives. The slurry, with most of the bitumen from the sand particles, in a diluted form, with low specific gravity, is then mixed with a large amount of water into a separation vessel, where most of the sand particles settle, the bitumen and diluent rise to the top and a middling aqueous stream, with fine silt and clay, is withdrawn.
The hot water process has several disadvantages:
The frothy oil is a hard to break emulsion and needs a relatively expansive cleaning stage, with high energy requirements and bitumen losses.
About 25-30% of bitumen is entrained in the middlings, requiring supplementary costs and energy supply within a secondary process stage.
Important heat losses within the aqueous and sand tailings, practically non settling in the tailing ponds; this means important pond surface, water and energy requirements.
Regarding the cold water processes the main disadvantage is the loss of expensive diluent within the sand tailings.
Another disadvantage is the high water requirement and the fact that waste streams contain pollutants.
To solve the above mentioned disadvantages and to improve the processes several processes have been proposed:
U.S. Pat. No. 4,120,777 claims a process including mildly heating the tar sands mixture with water to about 85.degree.-95.degree. F., in the presence of an alkali metal bicarbonate to warm the mixture to about 100.degree.-130.degree. F. and then recovering bituminous material from the sand, at this temperature, substantially lower than about 180.degree. F. in the hot-water process.
U.S. Pat. No. 3,986,592 claims a cell designed for use in the hot water process comprising a tank with a rotary shaft provided with a sand rake, positioned so as to move settled sand, and two or more deflecting baffles as to provide sufficient residence time in water.
U.S. Pat. No. 4,107,029 claims a process to control the withdrawal rate of the tailings from the hot water primary separation vessel, with a rake torque sensor for the low fines feed and a density gauge for the high fines feed, to better stabilize the separation process and to reach higher yielding of the bitumen in the froth.
U.S. Pat. No. 2,965,557 claims a process for recovering oil and silt from bituminous sand, which comprises: introducing a bituminous sand-diluent mixture into a separation zone to form a lower fluidized bed of sand and an upper liquid layer of oil and silt, injecting large quantities of hydrocarbon diluent into the above mentioned lower bed; pumping the lower product, diluted with water, to a sand washing zone, to form a lower fluidized bed of sand, a water middling and an upper liquid layer of hydrocarbons.
U.S. Pat. No. 4,017,377 claims a process for recovering oil from tar sands, including the steps of: subjecting the sand to a diluent to reduce viscosity of the oil layers surrounding each sand particle; bringing the pre-soaked sand in an aqueous bath having a slightly raised specific gravity and a wetting agent, the released droplets of oil to be rapidly accelerated to the water surface, while the cleaned sand settles to the bottom.
U.S. Pat. No. 4,067,796 claims an improved process for bitumen recovery from tar sand, employing a vessel containing a liquid comprising an organic phase, consisting of a hydrocarbon diluent, and an aqueous phase. This vessel is provided with means of mechanical mixing. Tar sand is introduced into the said vessel, including the mentioned hydrocarbon diluent, at a temperature of 110.degree.-150.degree. F. fresh solvent below the solvent-water interface and fresh water above the bottom of the vessel
U.S. Pat. No. 3,941,679 claims an anhydrous process for separating oil from bituminous sand using as diluent trichlorfluormethane (Freon 11), circulating in counter-current with the sand in helical type conveyors.
U.S. Pat. No. 3,875,046 claims a process for extracting oil from tar sand containing fines in a closed-cycle, single stage, using only one extraction vessel in which tar sand is contacted with diluent, steam and hot water containing process control additives, in fluidized bed condition. The cleaned sand is washed in counter-current as to recover heat and additives.